The objective of this project is to study the microbial flora of the cancer patient; i.e., to determine acquisition, colonization and subsequent infection. Routine surveillance cultures of patients determine which organisms are acquired. New and unusual organisms are extensively studied. Proteus spp. and Serratia are subspeciated to specifically identify strains. Acquired organisms more frequently cause infection than the original patient flora. Approximately 90% of cancer patients have 1 to 4 species of yeasts during their hospital stay. Over half of these yeasts are acquired during the period patients are in the hospital. Patients colonized with C. tropicalis are more prone to bacteremia than those colonized with C. albicans. The combined effect of cancer chemotherapeutic agents and antibiotics on organisms that commonly cause infection is under analysis.